Process for preparing acrylic fibers

ABSTRACT

LOW STRENGTH ACRYLIC FIBER HAVING, UPON BOIL-OFF, A SUBSTANTIALLY STRAIGHT CONFIGURATION AND SPECIFIC SHRINKAGE, CHARACTERISTICS IS DISCLOSED. THE FIBER IS PREPARED BY WASHING AND DRAWING FRESHLY SPUN ACRYLIC FILAMENTS, AND PLASTICIZING THEM UNDER RESTRAINT TO RELAX THE FILAMENTS. THIS FIBER, COMBINED THAT HIGH STRENGTH, HIGH SHRINKAGE FIBER, IS USED TO PROVIDE PILL-RESISTANT, BULKED, COMPOSITE YARNS AND FABRICS THEREOF, HAVING EXCELLENT AESTHETICS.

J. F. RYAN, JR

PROCESS FOR PREPARING ACRYLIC FIBERS Original Filed Sept. 28. 1966 Feb. 2,1971

United States Patent 3,560,603 PROCESS FOR PREPARING ACRYLIC FIBERS James Francis Ryan, Jr., deceased, late of Westover Hills, Va., by First and Merchants National Bank of Virginia, administrator, assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Application Sept. 28, 1966, Ser. No. 582,482, which is a continuation-in-part of application Ser. No. 480,730, Aug. 18, 1965, which in turn is a continuation-in-part of abandoned application Ser. No. 307,822, Sept. 10, 1963. Divided and this application Jan. 9, 1969, Ser.

Int. Cl. D01d 5/22 US. Cl. 264-168 7 Claims ABSTRACT OF THE DISCLOSURE This application is a divisional of my copending application Ser. No. 582,482, filed Sept. 28, 1966, now US. Pat. No. 3,438,192, issued Apr. 15, 1969, which is a continuation-in-part of my application S.N. 480,730, filed Aug. 18, 1965, now abandoned, which in turn is a continuation-in-part of my copending application Ser. No. 307,- 822, filed Sept. 10, 1963, now abandoned.

SPECIFICATION This invention relates to improved acrylic staple and tow and to structures of superior tacility and freedom from surface distortion made therefrom.

Fibers of acrylonitrile polymers are more wool-like than most other synthetic fibers. They have many advantages over wool such as the abilit to be washed without shrinking, resistance to insects, and the capacity of being easily dyed to bright and fast shades.

Some animal fibers have a superior smooth tactility which is in large measure due to freedom from sharp bends or crimp. Such a fiber is difficult to process in ordinary textile manufacturing due to deficiency in the interfiber cohesiveness needed in the early staple processing steps such as picking, carding and first drafting. Such fiber frequently is lost to an excessive degree from its fabrics (sheds excessively) for the same reason. Moreovei, the most luxurious smooth-tactility fibers, such as mohair and cashmere, have natural surface modifiers which soften" the fiber, providing a somewhat slippery feel. This combination of straightness and surface modification accounts for the substantial advantage of certain natural fibers over synthetic fibers in commercially important, luxury markets, despite the practical disadvantages resulting from low interfiber cohesiveness. It would be highly advantageous to combine the luxurious characteristics of certain animal fibers with the superior ,durability and carefree utility of the acrylic fibers.

The acrylonitrile fibers used heretofore in classic knit sweaters resulted in sweaters that exhibit surface distortion (developed pills) as the result of the abrasive action encountered during wear. Pills are small balls or fluffs of fibers which are rather tenaciously held on the surface and thereby detract from the attractiveness of garments. The acrylonitrile fibers have also lacked the smooth slick feel of some natural fibers.

Many efforts have been made to overcome the pilling 3,560,603 Patented Feb. 2, 1971 of synthetic fibers. Pilling can be decreased by highly twisting the yarns, but this greatly decreases the bulk and cover, and strongly modifies the aesthetics of knit fabrics. Both lubricating and slip-proofing finishes have been tried with only slight improvement. Furthermore, any such improvement is only temporary since finishes with such characteristics which are generally available are removed by only a few washings or dry cleanings.

The blending of lowand high-shrinkage fibers to obtain bulky yarns and fabrics is not new, and is taught, for example, in US. Pats. 2,810,281 and 2,985,940. However, fabrics made from such blends, especially bulky-knit fabrics, heretofore have suffered from pilling and from a lack of smoothness and slickness. For these reasons the use of such blends has been limited.

Likewise, bulky fabrics have been made from composite fibers. These are fibers spun from two different polymers or copolymers in a side-by-side or sheath-core relationship along the length of the fiber; they differ from homofibers which are spun from a single polymer or copolymer in that because of an established difference in shrinkability between the two components of the composite fiber, they develop a spiral crimp on boil-off in water, for example, which results in bulky yarns and fabrics. One method of preparing such fibers is described in US. Pat. 3,038,236. But such fibers yield fabrics which are not optimum for many uses because of severe pilling and harsh tactile qualities.

The present invention provides a process for producing acrylic staple fiber having good textile processibility, and exceptional straightness in the final structure. It further provides a straight fiber with durable soft-slick tactility. It still further provides bulky knit fabrics of acrylic fibers having in combination the fine aesthetics of animal fibers and relative freedom from pilling during normal wear. It also provides novel composite yarn which is especially suitable for preparing knit fabrics of the foregoing qualities.

These and other advantages are attained in an acrylic staple having, preferably, a temporary and a permanent configuration, the temporary configuration comprising 3 to 15 crimps per inch for good textile processibility, the permanent configuration being developed from the temporary configuration by boil-off in water and being characterized by a straightness factor, SF, of 0.70 to 1.50, an initial shrinkage temperature, IS, of at least 145 C., and a maximum shrinkage force factor, MSF, of no more than 0.9. By forming yarn blends that include at least 25 weight percent of such fiber, the unique utility of the fiber can be attained in the blend. These yarn blends can be bulked in skein or fabric form, and in either practice the defined staple becomes the predominant surface fiber. In general, this acrylic staple is produced by spinning acrylic filaments, simultaneously washing the spun filaments to reduce spinning solution solvent to below about 5 percent and drawing to 120 to 450 percent, preferably 120 to 300 percent, of the as-spun length, relaxing the drawn filaments to the extent of 2 to 40 percent, preferably 15 to 40 percent, of the drawn length by exposure to plasticizing conditions preferably for at least 0.5 second while restrained by a force of at least 5 milligrams per denier (mg/den), optionally mechanically crimping at a temperature no higher than 20 C.

below the Tg of the fiber to 3 to 15 crimps per inch and removing any plasticizing material. In this specification the term acrylic staple means staple comprising at least percent by weight of polymerized acrylonitrile in the polymer. It will be seen that the plasticized taut relaxation is an important element of the processing sequence leading to new acrylic fibers which provide the lasting luxurious surface characteristics desired in classic knit sweaters.

The properties of the acrylic staple in the second or permanent state are determined on the staple that is drawn, relaxed as described and crimped to 3 to 15 crimps per inch. Details of the tests are:

The straightness factor, SF, is determined as follows:

(1) Approximately one gram of the staple to be tested, having a cut length of approximately 3 inch (7.6 cm.), is hand-carded.

(2) 0.5 gram of the fiber is accurately weighed.

(3) Approximately 250 ml. distilled water is placed in a 400 ml. beaker, and the weighed sample of fiber is dropped onto the surface of the water in as open a manner as possible. It may be necessary at this point, particularly if a hydrophobic surface modifier is present, to add a few drops of a wetting agent to assure complete wetting of the sample.

(4) The beaker is covered with a watch glass and immersed completely in a stream bath for 40 minutes.

(5) The beaker is removed from the steam bath and allowed to cool to 30 C. or lower.

(6) The sample is removed from the beaker with a glass rod, laid on a paper towel without distorting its configuration, and allowed to dry.

(7) Eight clumps of filaments are selected at random from the dried fiber and laid on a black velvet surface. One filament is selected from each bundle.

(8) Pieces of masking tape are cut to a size which weigh 2 mg./denier (calculated on the filament to be tested). One piece is attached to each end of each of the 8 selected filaments.

'(9) One of the pieces of masking tape, with the filament attached thereto, is attached to one end of a microscope slide. The filament is permitted to hang under the weight of the second piece of masking tape, and then the second piece of masking tape is attached to the microscope slide. A piece of flat, flexible film having reference marks one-inch apart is placed on the filament. The filament is examined under th emicroscope by comparing it with inscriptions on a transparent overlay representing Partial Circles of Vita, 3&2, V64, /128 /256, and /508 inch radii, coded 8 through 1, respectively.

(10) Each of the curvature found within a one-inch length of the fiber sample is matched with one of the standard curvatures on the overlay and assigned a number code.

(11) The mean curvature of each individual sample of fiber is calculated as the average of the one or more numbers recorded representing the curvatures observed. The number of curvatures observed for each sample is also recorded.

(12) The mean curvature, R, of the overall sample is calculated by averaging the mean curvatures of the eight filaments.

(13) The mean frequency, f, of curvatures of the overall sample is calculated by averaging the number of curvatures per inch of filament in the 8 filaments.

(14) The straightness Factor, SP, is calculated as follows:

f w den.

The initial shrinkage temperature, IS, is determined by mounting a bundle of fibers of about 100 denier between the jaws of an Instron and separating the jaws until a tension of about 0.3 gm. is indicated. With the jaws held at this position, the temperature of the air surrounding the fiber bundle is raised approximately 10 C. per minute. The stress and temperature are recorded as function of time, and a plot of temperature, t, versus stress is prepared. The temperature, T, at which additional stress first appears is noted on the plot. Initial Shrinkage Temperature, IS, is calculated as follows:

It is also noted that the stress developed with increase in temperature reaches a maximum after which further increase in temperature results in lower stress, presumably due to inter-molecular rearrangements. The value of the stress at the maximum is used to calculate the Maximum Shrinkage Force Factor, MSF, by the following equation:

Max. Stress (qms.)

MFS: denier of bundle A yarn blend is provided in one embodiment of the invention which includes at least weight percent of the acrylic staple. I have found that some of the most serious aesthetic limitations of synthetic fibers in apparel and other utility can be overcome by blending with a highly shrinkable fiber, my low shrinkage fiber which, on boiloff, orients as a crimp-free fiber predominantly at and near the surface of the yarn which bulks as the highly shrinkable component retracts. In a preferred embodiment the staple or tow of this invention has an initial mechanical crimp which aids in textile processing but which is lost on boil-off at any convenient stage of processing, as in yarn or fabric form. In a further preferred embodiment, the fiber of this invention is stretched only to r 120 to 300% of its as-spun length in manufacture, which imparts low-entanglement tendency.

When these fibers are taut-relaxed as described herein, they exhibit a remarkable resistance to development of crimp. The fibers can be crimped, as by stulfer-box crimping of the tow before it is cut into staple, while retaining their ability to lose most or all of this crimp during a subsequent hot-wet treatment. Thus, such fibers may be in the crimped state during carding and spinning but when fabrics containing the fibers are treated in a hot-wet process, as in dyeing, the crimp will substantially disappear. The straight fibers confer to their fabrics a smooth, slick feel by orienting to the surface of the yarns.

Fibers as normally prepared have, after drawing a substantial potential shrinkage. When this shrinkage is permitted to occur in an uncontrolled manner, crimp will develop due to the non-uniform drawing stresses always present in the yarn. By allowing shrinkage to occur under a restraint of at least 5 mg./den. and under plasticizing conditions which permit the fiber to shrink, internal stresses are reduced or eliminated without crimping, and the straight configuration remains. Depending on the characteristics of the particular fiber being processed, the conditions required for plasticizing during the relaxation step may be chosen from among passage over heated rolls, hot air, stream of either atmospheric or higher pressure, refluxing organic vapors, vapors from a refluxing mixture of an organic solvent and water, etc. The essential requirement is that the conditions established and the time of exposure be selected such that the fiber will relax to the extent of 2 to 40%, preferably 15 to 40% of its as-drawn length while being restrained by a load of at least 5 milligrams per denier, as, for example, 5 to milligrams per denier. Exposure of the drawn acrylic filaments to plasticizing conditions for a contact time as low as 0.01 second is suitable provided that the plasticizing conditions are suflicient to relax the filaments to the extent of 2- under a restraint of at least 5 milligrams per denier. Preferably, the filaments, are exposed to the plasticizing conditions for at least about 0.1 second. Contact times of at least about 0.5 second are especially desired because the filaments can be handled very smoothly with exteremly low turbulence.

The second fiber in the blend may be any high-strength fiber which has a relatively high shrinkability. Examples of operable embodiments are found among the acrylic and modacrylic fibers which have been relaxed only partially after drawing or which have been handled in such a way as to retain substantially all of the potential shrinkability developed during the drawing process. Alternatively, a completely relaxed tow may be processed on the Turbo Stapler, Pacific Converter or other such device to a highshrinkage sliver and blended, without prior relaxation, with the low shrinkage fiber. For example, a fiber representing a copolymer of acrylonitrile and sodium styrenesulfonate in a ratio of 94/6 to 99/1 is particularly suitable, as are the copolymers of acrylonitrile and a vinyl pyridine, the terpolymers of acrylonitrile, methylacrylate and sodium styrenesulfonate; the modacrylics, which may have substantially more than 15% modification by a non-ionic modifier such as vinyl acetate, methyl acrylate, vinylidene chloride, styrene, other vinylactive, copolymerizable monomers, or ionic modifiers such as sodium styrenesulfonate or a vinyl pyridine, and multicomponent, composite filaments prepared in such a way and being of such a composition as to be self-crimpable on exposure to a boiling scour also can be used. The essential requirement is that the high shrinkage fiber have sufiicient potential shrinkage as it exists in the blend to produce the desired degree of bulking. It is well -known in the art to select a high shrinkage fiber suitable for properties desired in the final yarn or fabric. All the foregoing compositions with the exception of the modacrylics and the composite or bicomponent fibers can be used in preparing my new lowshrinkage staple.

Two types of fibers are blended together to form a single yarn. Blends containing from to 75% of the high-shrinkage fiber and from 90 to 25% of the tautrelaxed fiber have been found satisfactory for the purpose of the present invention. The low-shrinkage fiber concentration is thus about 25% or more. It is important, however, to use enough of the high-shrinkage fiber to result in suitable bulking of the low-shrinkage fiber. The preferred ranges for the blends of high-shrinkage fiber and low-shrinkage fiber are to 50% and 85% to 50% respectively.

Blending of the highand low-shrinkage fibers may be accomplished in a variety of ways, such as in the picker or draw frame processing, if both fibers are originally in staple form. Either pin drafting or the Hood Doubler may be more convenient if one of the fibers has previously been processed on the Turbo Stapler or Pacific Converter. The blended slivers are processed into yarn by any available means. The resulting yarn may be made into skeins and treated with steam or hot water to shrink and crimp the high-shrinkage fiber, or the yarn may first be knitted into fabrics. In the latter case the shrinkage will be accomplished during scouring and dyeing of the fabric.

One embodiment of composite yarn produced by the above process is schematically illustrated in FIG. 1, which represents a longitudinal section of the yarn on an exaggerated scale. Whenever shrinkage occurs, the non-shrinking homofibers are bulked and tend to be pushed to the surface, as illustrated at 1. These fibers do not have the frequent, sharp crimps of the composite fibers 2 making up the core, and, hence, have less tendency to become entangled to form pills. But, more importantly, these surface fibers have the benefit of the taut relaxation of this invention and being substantially straight have a considerably lower tendency to entangle than is characteristic of the crimped fibers. For this reason fabrics made from such yarns have little or no tendency to develop pills. Furthermore, the lack of appreciable crimp in these surface fibers results in fabrics having a smooth, slick, pleasnt tactility.

It will be noted that although I refer to fibers 1 and 2 of FIG. 1 as the outer sheath and inner core, it will be appreciated that the two types of fiber are not sharply separted in the yarn. The core and sheath fibers blend into each other by a zone of intertwined fibers of both types, which compels the yarn to move or stretch as a unit without physical separation of the sheath from the core.

The yarn blend of this invention yields fabrics which are not only non-pilling but which have good durability to wear, exceeding the durability of comparable fabrics made from natural fibers. By means of this invention,

6 therefore, the combination of high bulk, pleasing aesthetic properties, good durabiltiy and freedom from serious pilling problems is attained.

As will be illustrated in the examples, further improvement in the desirable tactility of the fibers, yarns and fabrics of this invention may be obtained by use of a suitable surface modifier. It is known to apply such modifiers which are relatively easily removed by laundering or dry cleaning. It is preferred in the process and product of this invention that the modifier be selected from those which are retained by the fiber through textile processing thereof and through launderings and dry cleanings of the fabrics produced thereupon. A very close approximation of the tactility of animal fibers is obtained by the combination of the exceptionally straight, surface-oriented fiber of this invention and a suitable wash-resistant surface modifier which confers a smooth or slick tactility.

While the fibers of any cross-section may be employed advantageously in the process of this invention, such as for example the usual dogbone and crenulated round fibers, it has been found that an additional improvement in certain aesthetic properties may be obtained by use of a trilobal, or cloverleaf, cross-section.

Without limiting this invention, the following examples are given. Percentages and parts are by weight unless otherwise apparent.

Example I Part 1.-A copolymer is prepared containing 96% acrylonitrile (AN) and 4% sodium styrenesulfonate (SSS). The copolymer is dissolved in dimethylformamide (DMF) to give a 27% solution. The solution is dry-spun by a process substantially as described in the Flannagan US. Pat. 2,615,198. The resulting filaments are washed in water at C., While being drawn to 2.5 times their spun length, and passed through a chamber containing super-heated steam at C. where 33% relaxation occurs in 3.75 seconds under a tension of10 mg. per denier to give filaments of 12 denier. A tow of the fibers, with a total denier of 470,000, is then crimped in a stuffer-box crimper to a level of 4.9 crimps per inch and 3.7 crimp index after which it is treated with a commercial lubricating finish. The tow is cut into staple fiber varying in length from 3- to S-inches. The staple is dried at 130 C. and carded on a worsted card to form a sliver weighing 165 grains per yard (9.8 gms. per meter). This is referred to as Fiber A. This fiber has the following properties:

Straightness factor, SF 0.82 Initial shrinkage temp., IS 165 Maximum shrinkage force factor, MSF 0.3

By omitting the relaxation step while maintaining all other processing steps the same as for Fiber A, a fiber is obtained which has the following properties:

SF 0.58 IS MSF 1.3

Part 2.Another filament is similarly spun from a terpolymer consisting of 89.6% acrylonitrile, 5.7% methyl acrylate (MA) and 4.7% 2-methyl-5-vinyl pyridine. The washed filaments are drawn to 4 times their spun length yielding filaments of 3 denier. The filaments, as a tow, are crimped in a stuffer-box crimper and then dried in a tunnel oven at C. for 15 minutes. The dried tow is processed on the Turbo Stapler with a hot stretch of 1.78 at a temperature of 138 C. It is cooled, stretchbroken and mechanically crimped to yield a sliver weighing 140 grains per yard (8.3 grns. per meter). This is referred to as Fiber B.

Fiber A has a shrinkage of 1% when boiled off.

Fiber B has a shrinkage of 40%.

Part 3.Ten slivers of Fiber A are combined with 5 slivers of Fiber B and the combined slivers passed through a Hood Doubler to reduce their maximum staple length to 6 inches or less. Four of the resulting slivers are combined and passed through a pin drafter to form one sliver, and four of the latter type are passed through another pin drafter and finally spun into a 2/9 worsted count yarn having Z turns per inch twist in singles and 2.55 turns per inch in the ply. Skeins prepared from this yarn are dyed at the boil using both acid and basic dyes so as to dye both fibers. After drying, this yarn is knit on a 3 /2-cut Stoll knitting machine in a halfcardigan pattern.

The dyeing operation at the boil causes the Fiber B to shrink and migrate to the core of the yarn and causes Fiber A to bulk on the surface. The finished fabric is resilient and lofty with a smooth, slick feel. The surface fibers are essentially straight with very little crimp. When tested for pill resistance by ASTM Test D1375 (ASTM Standards, 1959 Supplement, Part 10, page 173) a rating of 3.5 is obtained. In this test the number of pills per square inch is determined and the fabrics are rated on a scale from 1-5, where 5 represents no pilling and 1 represents severe pilling. A fabric with a rating of 3 or better is considered satisfactory.

Part 4.-A surface modifier is applied to the tow of this example as followsi Ten parts of a commercial 100% polyepoxide are added to 257 parts of water and stirred until solution is completed except for slight cloudiness. Then 133 parts of a commercial 30% silicone resin (in aqueous dispersion) are added with stirring. This emulsion is applied to 470,000 denier crimped tow of Part A, the amount of emulsion applied being approximately 1 part of emulsion to parts of tow (calculated to leave 1% silicone and 0.25% epoxide on the fiber). The wet tow is then cut to 3- to 5-inch staple and dried by heating at 130 C. for minutes. This is identified as Fiber A-M.

Fabrics comprising the surface-modified fibers approach those comprising the luxury animal fibers even more closely in tactility. These desirable aesthetics are durable to multiple dry cleanings and/ or launderings.

Example II Part 1.A copolymer is prepared containing 96% acrylonitrile and 4% sodium styrenesulfonate. The copolymer is dissolved in dimethylformamide to give a 27% solution. The solution is spun as in Example I. The resulting filaments are washed in water at 95 C., while being drawn to 1.8 times their spun length, and passed through a chamber containing superheated steam at 130 C. where 28% relaxation occurs in 1.04 seconds under a tension of 10 mg. per denier to give filaments of 3.5

denier. The fibers, in the form of a tow with a total denier of 470,000, are crimped as in Example I, Part 1, to a level of 8.6 crimps/ inch, 4.8 crimp index, in a stufferbox crimper, and surface-modified as described in Example I, Part 4.

The tow is cut into staple fiber varying in length from 3 to 5 inches. The staple is dried, and carded on a worsted card to form a sliver weighing 165 grans per yard (9.8 gm. per meter). This is identified as Fiber CM.

A similar fiber is prepared except that the taut relaxation step is omitted. It is dried at 130 C. to result in a residual shrinkage of less than 4%. The filaments had the following properties:

Fiber without Fiber CM relaxation SF 0. 99 0. 60 IS 145 125 MSF 0. 8 1. 5

8 surface-modified as described in Example I, Part 4 cut into 3- to 5-inch staple, and dried in a tunnel oven at 70 to C. for 15 minutes. The dried staple is processed on a worsted card to form a sliver weighing 140 grains per yard. This is identified as Fiber DM.

Fiber CM has a shrinkage of 1% when boiled off.

Fiber DM has a shrinkage of 27% and an SF of 0.58.

Part 3.Ten slivers of Fiber CM are combined with 5 slivers of Fiber DM and the combined slivers are passed through a pin drafter. Four of the resulting slivers are combined and passed through a pin drafter to form one sliver, and four of the latter type are passed through another pin drafter and finally spun into 12 cotton count yarn having 7.5Z turns-per-inch twist. This yarn is knit on a 12-cut Jacquard knitting machine in a loose pattern (10 courses per inch). The fabric is piece-dyed at the boil using basic dyes to dye both fibers.

The dyeing operation at the boil causes the Fiber DM to shrink and migrate to the core of the yarn and causes Fiber CM to bulk on the surface. The finished fabric is resilient and lofty with a smooth, slick feel. The surface fibers have very little crimp. When tested for pill resistance by ASTM Test D1375, a rating of 3.0 obtained.

Fabric prepared in the same manner but using the fiber without taut relaxation in place of Fiber CM is less resilient and lofty, has a less smooth-slick feel and is rated 2.0 when tested for pilling resistance.

Example III Part 1.-Filaments are prepared as in Example II, Part 1 except that the spun filamentsare drawn to 210% of their spun length. The final denier per filament is 6, the crimp frequency 5.7/inch and crimp index 4.5. Exposure to relaxation is 1.8 seconds.

The properties of this product, Fiber E, and a similar fiber prepared without the relaxation are as follows:

Fiber without Fiber E relaxation SF 0. 87 0. 55 IS 150 123 MSF 0. 6 2. 4

The preparation of acrylic fibers which are inherently straight, i.e., do not develop crimps and kinks in normal wetting and drying cycles, requires control of fiber tension, time of exposure and plasticizing conditions employed in the relaxation step. The composition of the acrylic polymer used to prepare the spun filaments influences the conditions required to produce inherently straight fibers.

The fibers used in the following experiments, shown in Table I, are all prepared by the process of Example I, using the indicated polymers. The resulting filaments are washed in water at C., while being drawn to the indicated extent before the relaxation step. In this table, as elsewhere in the specification, the term X is employed to indicate the factor employed in drawing. For example, 3X means the fiber was drawn to 300% of its undrawn length. After relaxation, the filaments are given a mild crimp in the stuffer-box crimper, then cut to staple and dried in a tunnel oven at C.

TABLE I Relaxation conditions Properties Draw Fiber Steam Tension, Time, Percent Polymer ratio denier temp.,C. mg./den. seconds i'eilax- SF IS MSF axon AN/SSS 96/4 3X 12 Samgas above 3X 12 AN/MA/MVP swan 4.7---- Same as above 9 1 Percent spinning solution solids=31.7.

Example V Some acrylic filaments which are low in combined hydrophillic monomer do not respond to the limited steam relaxation treatments shown in Example IV as is illustrated by the first terpolymer of that example. Alternate methods for the relaxation of these acrylic filaments have been found by using the vapors from a mixture of water and a solvent for the polymer.

The filaments for these tests, shown in Table II, are spun as in Example I, all being drawn to 2.5 times their spun length. Tows of about 1000 total denier are ten sioned by attaching weights and then are exposed for 5 seconds to the vapors above boiling vessels of a 50/50 mixture of dimethylformamide and water, or an 80/20 mixture of dimethylformamide and water. The exposed filament bundles are cut to about 3 inch lengths and dried at 130 C. The dried fibers are tested for fiber straightness factor, SF, with results shown in following table. As will be observed, these results show that a restraint of one milligram per denier is inadequate to maintain the fiber in a straight configuration in all cases. Higher restraints of 7 to 30 milligrams per denier are generally adequate provided suitable plasticizing conditions are employed.

of wear (25 hours) this desirable soft-slick handle is lost. The superiority of the high-shrinkage fiber of Example II is illustrated by the fact that the fabric of that example did not lose its attractive aesthetics during Wear periods of up to 350 hours.

In the low-twist bulky yarns used to prepare the fabrics of Example II and that above, some of the shrunken corefiber ends work up to the fabric surface during wear. The effect of these core-fiber ends is to dilute the straight surface-fibers. If the core-fibers themselves are relatively straight, and especially if they also have been surface modified, little change in fabric handle is produced, but if the core-fibers are not straight a rapid change in fabric handle takes place as they work up to the surface.

Measurements of fiber straightness gave the following results:

Fiber as B Example I, but 6 denier-4.43

Fiber as D-M Example II, but 6 denier-0.5 8

Example VII Part 1.Filaments are spun from a terpolymer consisting of 89.6% acrylonitrile, 5.7% methylacrylate and 4.7% 2-methyl-S-vinyl-pyridine. They are washed and drawn to 1.8 times their spun length and passed through a chamber TABLE II After exposure for 5 sec. to

vapor over boiling- Relaxation tension, No taut Polymer mg./dinier relaxation DMF/Water, 50

Polyacrylonitrile (AN AN/MA/SSS (93. 6/6. 0/0. 4)

DMF/water, 80/20 1 IS=; MSF=0.5. 2 IS=; MSF=O.3.

Example VI Fiber C-M of Example II, Part 1, is compared in two blends to illustrate influence of the high-shrinkage fiber on tactile aesthetics of fabrics. This fiber is blended with a six denier-per-filament fiber otherwise the equivalent of the 3-denier-per-filament fiber described in Example I, Part 2. A fabric is made from this fiber blend in the manner described in Example II, Part 3. This fabric initially has a desirable soft-slick handle, but after a short period are prepared. The conditions employed and SF values obtained are summarized in Table III.

5 20 N taut relaxation Part 2Other filaments are similarly prepared from a terpolymer consisting of 93.6% acrylonitrile, 6.0% methyl acrylate and 0.4% sodium styrenesulfonate. The washed filaments are drawn 4.5 times their spun length yielding filaments of 3 denier. The filaments are crimped in a stuffer-box crimper then dried in a tunnel oven at 130 C. for 15 minutes. The dried tow is procesed on a Turbo stapler with a hot stretch of 1.58 at a temperature of 132 C. It is cooled, stretch-broken and lightly crimped to yield a sliver weighing 140 grams per yard (8.3 gms. per inch). This fiber (G) has a shrinkage of 30% on boil-off in water.

Part 3.Slivers of Fiber F and Fiber G are processed separately through three stages of pin drafting. The sliver weights are adjusted on the final pass so that the sliver of Fiber F weighed 14.0 grains per yard and the sliver of Fiber G weighed 6.0 grains per yard. These two slivers are combined as fed to the spinning frame to produce a 9 worsted-count yarn with Z turns per inch twist. Two ends of this yarn are plied with 2.55 turns per inch. The plied yarn is skein dyed at the boil using both acid and basic dyes to dye both fibers. After drying, the yarn is knit on a 3 /2-cut Stoll knitting machine in a loose, novelty pattern. The skein dyeing operation at the boil causes Fiber G to shrink and migrate to the core of the yarn and causes Fiber F to bulk and form loops on the yarn surface. The finished fabric is lofty and resilient with a smooth-slick handle.

Example VIII Filaments are spun from a copolymer of 96% acrylonitrile and 4% sodium styrenesulfonate. The spun filaments are combined into a tow of about 100,000 denier. The tow is passed through a series of tanks containing water at 95 to 98 C. During passage through the initial seven tanks, the tow is washed to a solvent level below 5% and drawn to 250% of its spun length. During the passage through the last two tanks and a coupled steam chamber at 100 to 105 C., the tow is allowed to relax in amounts varying from about 3 to about 22% of the drawn length. Experience teaches that under the conditions of this example the tension on the tow is in the range of to mg. per denier. The tow is crimped in a stufier-box crimper, cut to staple varying in length from 3 to 5 inches and dried at 130 C. The resulting staple fibers have straightness factors, SF, between 0.82 and 1.05. They are blended in the ratio of 70/30 with Fiber B of Example I and processed as in Part 3 of that example to make knit fabrics with desirable loft, resilience and smooth-slick tactile aesthetics.

Example IX Filaments are spun from a copolymer of 96% acrylonitrile and 4% sodium styrenesulfonate. The washed filaments are drawn to 1.5 times their spun length. The wet drawn filaments are divided into three parts. One part is passed through a chamber containing superheated steam at C. with tension of 10 mg. per denier to obtain 27% relaxation. The second part is passed through an apparatus consisting of a set of metering input rolls, six adjustable-speed, heated rolls and a package windup. When the temperature of the rolls is adjusted to 175 C., the speeds are adjusted to allow 26% taut relaxation. The third part is given no taut relaxation treatment. All parts are crimped mildly in a stufler-box crimper, cut to staple of about 4-inch length, and dried at 130 C.

The straightness factors of the staple fibers are as follows:

No relaxation 0.62 Relaxation in steam 0.94 Relaxation on hot rolls 0.79

Knit fabrics are prepared from these fibers blended with the high shrinkage fiber of Example I in the manner described in Part 3 of that example. The fabrics made from the fibers relaxed in steam or on hot rolls were smoother, slicker and had better loft and resilience than the fabric made from the fiber with no taut relaxation.

Example X Part 1.A composite filament is spun by the method of US. Pat. 3,038,236 using the following polymers:

(I) 100 polyacrylonitrile; (II) 96% acrylonitrile/4% sodium styrenesulfonate copolymer.

These two polymer compositions are spun together sideby-side, in about equal proportions by weight, to form a composite filament. The spun filaments are washed in hot water while being drawn to four times their spun length and dried. The dried tow has a filament denier of 6 and a total denier of 470,000. This tow is hotstretched on the Turbo Stapler to 2.12 times its previously drawn length. When boiled off, a sample shows a shrinkage of 20%. This will be referred to as Fiber H.

Part 2.Same as described in Example II, Part 1.

Part 3.A sliver of Fiber H and a sliver of Fiber CM are combined and run through the Hood Doubler for the purpose of blending and breaking to less than 6- inch staple. The resulting sliver comprising 60 parts of Fiber CM and 40 parts of Fiber H is combined with four other similar slivers and run through a pin drafter. Again, four slivers are combined and passed through the pin drafter and finally spun to 20 cotton count (30 Tex) yarns of 11Z turns per inch twist. Two of these yarns are plied and the two-ply yarn is twisted 4.7S turns per inch. The plied yarn is knit into fabric on a 21-gauge full-fashion machine. The finished fabric weighs 7 02/ sq. yd. (234 gm./sq. meter) and has a construction of 25 (courses) x 17 (wales).

The pill resistance of this fabric is determined, by ASTM Test D-1375 to be 4.6. The fabric has a pleasant, smooth, slick feel to the hand.

Example XI A composite filament is spun.by the method of Example X using the following polymers:

(I) 100% polyacrylonitrile, (II) 94.45% acrylonitrile/5.55% sodium styrenesulfonate copolymer.

These two polymers compositions are spun together side-by-side, in a ratio of about 3 parts of I to 1 part of II, to form a composite filament. The spun filaments are washed in hot water, drawn 2.1 times their spun length, cut to staple of 3- to 5-inch length and dried at C. Other portions of the spun filaments are l3 washed in hot water, drawn 2.5 times their spun length, cut to staple of 3- to 5-inch length and dried. The filaments in each instance are 3 denier.

Some of the filaments after drawing are passed through a chamber containing superheated steam at 130 C. and a controlled 25% relaxation is allowed to occur.

By these variations in drawing and taut steam relaxing, composite filaments are obtained which develop different levels of crimp frequency (Cpi) and crimp index (C.I.) after boil-oflr'.

Crimp frequency is the number of crimps per inch.

(Crimp Index extended fiber length-relaxed fiber length X 100 extended fiber length Blends of these composite fibers with the Fiber C-M of Example II are made which contain 30% composite fiber. Yarns are made as described in Example II to cotton count with 7.1Z turns per inch. These yarns are knit on a 12-cut Wildman knitting machine at 15 courses per inch. The fabrics are piece-dyed at the boil using basic dyes. The dyeing operation causes the composite fibers to develop crimp 'which has an effect similar to shrinkage in the blend yarns.

The finished knit fabrics are compared by a panel of judges and rated for softness and resilience with the following results shown in Table IV. All fabrics are 6.5 to 7.0 oz./sq. yd.

1 Ratings on basis: softness of wool=0, eashmere=4. Ratings on basis: Resilience or woo1= 5, cashmere=2, cott0n=0.

Example X'II Copolymers of acrylonitrile dissolved in dimethylformamide are spun into fibers with a cross-sectional shape similar to a flattened tube with a Width to thickness ratio of about 3 to 1. These fibers have a preferred bending plane and, therefore, do not exhibit the stiffness and resilience of fibers with a more symmetrical cross-sectional shape.

To obtain fibers with improved stiffness and resilience, spinnerets with a cluster of 4 small holes for each filament are made. The small holes are arranged with one at the center and the other three spaced equally and symmetrically around the center hole. Spinnerets are made in which the diameter of the individual holes, the length to diameter ratio of the holes, and the spacing of the holes are varied. These spinnerets are used to prepare fibers from a 27% solution in dimethylformamide of a copolymer of 1.5 intrinsic viscosity of 96% acrylonitrile and 4% sodium styrenesulfonate. The conditions for spinning the filaments are varied and the number of filaments obtained as trilobal shapes from the coalescing of the 4 individual streams from the cluster of holes is observed. The results are shown in Table V.

TABLE V Spinning conditions Solution, C.

Aspfl, lb./hr. Spinneret (30 clusters of holes) 37 37 50 37 50 Percent trilobal filaments Other conditions held constant included.Spinning speed=300 2 Asp. is inert aspiration gas.

The spun yarns having more than 90% trilobal filaments are washed in water at 95 C. While being drawn to 2.5 times their spun length, passed through a chamber containing super-heated steam at 130 C. where relaxation of 32% occurs in 3.75 seconds under tension of 10 mg. per denier to give filaments of 12 denier. The filaments in the form of a tow are crimped in a stutter box crimper to about 6 crimps per inch, cut to staple fiber having 4 inch length and dried at 130 C.

When made into a yarn blend with Fiber B and knit to fabric in the manner described in Example I, the knit fabrics are more resilient than those produced in Example I.

From the foregoing, it is evident that the present invention constitutes a significant and broad advance in providing synthetic fibers for applications commonly employing luxurious animal fibers. From the examples it is apparent that the acrylic fiber, which upon boil-off serves as a relatively straight surface fiber, can be made from diverse acrylic polymers, for example non-hydrophilics (Ex. V), hydrophilics (Exs. I and II), and terpolymers (Ex. VI). But in every instance, it is necessary to process the drawn fiber with the described relaxation while restrained and under suitable plasticizing conditions, which permits development of the relatively straight, low-shrinkage (preferably below 5 percent) fiber. The high-shrinkage fiber can be made from the same materials as Well as others such as modacrylics, bicomponents and the like. Preferably the high-shrinkage fiber has a shrinkage of at least 15 percent, shrinkages being determined by boiling in Water for at least 15 minutes and then drying. It should be appreciated that in the instance of bicomponents, shrinkage means the effect of shortening by contraction plus shortening by development of the spiral crimp characteristic of such fibers. The fibers are of the usual denier for textile applications, and additional fibers in varying amounts my be included as long as they do not deleteriously affect the resulting products.

It will be apparent that various changes can be made from the detailed description of the invention without departing from its scope.

What is claimed is 1. A process for making acrylic fiber which upon boiloff has a straightness factor of 0.70 to 1.5, an initial shrinkage temperature of at least 145 C., and a maximum shrinkage force factor of no more than 0.9 comprising washing and drawing freshly spun acrylic homofiber filaments to to 450% of their as-spun length, and subjecting the drawn filaments to plasticizing conditions while under restraint of about 5 to 30 milligrams per denier to relax the filaments 2 to 40% of their asdrawn length.

2. A process in accordance with claim 1 wherein the said acrylic filaments are drawn to 120 to 300% of their as-spun length and are relaxed at 15 to 40% of their as-drawn length.

3. A process in accordance with claim 1 wherein the said drawn filaments are subjected to said plasticizing conditions for at least 0.1 second.

4. A process in accordance with claim 1 wherein the said drawn filaments are subjected to said plasticizing conditions for at least 0.5 second.

5. A process in accordance with claim 4 wherein the relaxed filaments are mechanically crimped to 3 to 15 crimps per inch.

6. A process in accordance with claim 4 in which the crimped fiber in staple length is formed into a sliver, and the resulting acrylic sliver is combined with sliver of high-shrinkage fiber to provide a yarn blend.

7. A process for making acrylic fiber comprising Washing and drawing freshly spun acrylic homofiber filaments to 120 to 450% of their as-spun length, subjecting the drawn filaments t plasticizing conditions while under restraint of about 5 to 30 milligrams per denier to relax the filaments 2 to 40% of their as-drawn length, and mechanically crimping the filaments at a temperature no higher than 20 C. below the 0g of the fiber to 3 to 15 crimps per inch.

References Cited UNITED STATES PATENTS Hare 264342UX Pitzl 264342UX Wishman 264342UX Knudsen et a1. 264342UX Nagata et a1. 264-182 Taniyama et a1. 264182 Maerov et a1. 264342UX Melchore et a1 8130.1X Bradley 264171 Gray et al 2876 Kovarik 2876 15 JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner US. Cl. X.R.

FYI-1950 UNITED STATES PATENT OFFICE 69 CERTIFICATE OF CORRECTION Patent No. 3,560,603 Dated FQDIUIBIJ 2, 1971 Inventor(s) It-1s certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

COlUIBD 15, line 2]., Claim 7, "08' sho ld read I gII Column 16, line '4, "3,000,222" should read 3,003,222

Signed and sealed this 22nd day of June 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents 

